A number of '''pseudo top-level domains''' to be used in naming computers have been defined at various times. These "pseudo-TLDs" include .bitnet, .csnet, .local, .onion and .uucp. Although these pseudo-TLDs look like Top-level_domains, and serve the same syntactic function in creating names for network endpoints, they have no meaning in the global Domain_Name_System and are (or were) used only for specialist purposes; typically for addressing machines that were not reachable via the Internet_Protocol for use in services such as E-mail and Usenet via UUCP. Although they have no official status, they are generally regarded as having been unofficially "grandfathered", and are unlikely ever to be allocated as top-level domains. .arpa is unique in having been a pseudo-top-level domain, formerly used by ARPA, that has now become a real top-level domain that is defined in the Internet_DNS_root for use as an Infrastructure_top-level_domain. {{GTLD}} *